I have set GREP_OPTIONS="--ignore-case --color" in ~/.bashrc as I normally want grep to work case-insensitive. However, there are times when I need grep to actually search case-sensitive, but the man page doesn´t suggest a param for this.

"command grep" : will launch the grep command (ie, the one found in the $PATH) even if there is an alias or functino with the same name. Usefull to prepend a "command" to actual command's use in alias and function definitions (and elsewhere when you want to bypass any eventual alias or function definition of the same cmd)
–
Olivier DulacMar 1 '13 at 13:15